Bluetooth-Enabled Danger Sign for Lab

[A Raymond] had some free time at work, and decided to spend it on creating a wireless warning sign. According to his blog profile, he is a PhD student in Applied Physics. His lab utilizes a high-powered laser system. His job is to use said system, but only after it’s brought online by faculty scientists. The status of the laser system is changed by a manual switchbox that controls the warning signs wired around the lab entrances. Unfortunately, if you were in the upstairs office, you only knew this after running downstairs to check. [A Raymond’s] admitted laziness finally got the better of him – he wanted a sign that displayed the laser’s status from the comfort of the office. He had an old sign he could use, but he wanted a way for it to communicate with the switchbox downstairs. After some thought, he decided Bluetooth was the way to go, using a pair of BlueSMiRF Bluetooth modules from Sparkfun and Arduino Uno R3’s.

He constructed a metal box that intercepted the cable from the main switchbox, mounting one BlueSMiRF and Uno into it. Upon learning that the switchbox sends 12V AC signals over three individual status wires, he half-wave rectified the wires and divided their voltages so that the Uno wouldn’t fry. Instead, it determined which status wire that had active voltage. and sent a “g(reen)”, “y(ellow)”, or “r(ed)” signal continuously via Bluetooth. On the receiving end, [A Raymond] gutted the sign and mounted the other BlueSMiRF and Uno into it along with some green, yellow, and red LEDs. The LEDs light up in response to the corresponding Bluetooth signal.

The result is a warning sign that is always up-to-date with the switchbox’s status. We’ve covered projects using Bluetooth before, from plush birds to cameras– [A Raymond’s] wireless sign is in good company. He notes that it’s “missing” a high pitched whining noise when the “Danger” lights are on. If he decides to add an accompanying (annoying) sound, he couldn’t go wrong with something like this. Regardless, we’re sure [A Raymond] is happy that he no longer has to go back and forth between floors before he can use the laser.

Right? A simple and logical solution is just to have a red light bulb outside the door that is tied to the laser’s power-power on. BT is garbage and I think we will all be laughing at it in about 3 years. Also (couldn’t resist from real genius) “always check your optics” ;)

“Whale song”? At least we know he’s a logical Vulcan. TBH, I was kind of confused for a second by the equation he used for the voltage divider. Never seen it in that form before. I might use that one day.

Just to clarify, this is a remote monitor of a safety system on *a different floor*. It would be cool if it failed safe, but people who install high-power lasers at universities know what they’re doing, as a rule. You can bet that downstairs there’s a much more reliable, fully fail-safe warning system, including a door interlock.

Anyhoo, great build quality there. Though you’ve missed out on a great chance to use one of those spinny red light things.

Even though this is just to let him know what the status is downstairs, and there are signs downstairs, fail safe or fail stupid (when it looses signal it turns off or makes some other notification) what this is really missing is big, red flashing lights on top for the danger signal!

personally i”m surprised he went through and spliced into the wires, seems like an awful lot of work that could have been handled by induction coils or even hall effect moniters. and would require less circuitry. To each their own though its still a good way to monitor from afar

Instead of streaming the status continuously, send a signal instantly on change and also a heartbeat signal that contains the status every, say, 10 seconds – with a timeout just over that in the receiving device. You get the benefit of instant notification of status change, very low bluetooth bandwidth and a worst case delay of 10 seconds if the link fails.

Didn’t any of the naysayers read this: “If the bluetooth connection is lost, the sign’s programmed to flip out and light up all the LEDs while attempting to re-establish the connection.” – So i see no problem in the sign losing the signal. Regarding tapping into existing signals, optocouplers is the way to go, then you are sure that your POS electronics doesn’t destroy some $100K electronic control box for the laser, down the line.